Despite decades of intense research, cancers remain a devastating set of diseases for which there is often no cure. The long term goal of this project is to identify small molecule therapeutics that block the secretion, and hence the functional expression, of multiple proteins involved in tumor angiogenesis and tumor cell survival. This conceptually novel approach for eliminating multiple cancer targets with a single drug relies upon the cotransins, a family of cell-permeable cyclodepsipeptides. Cotransins have recently been shown to potently inhibit the signal sequence-dependent cotranslational translocation into the endoplasmic reticulum (ER) of a small subset of secreted proteins, including vascular endothelial growth factor (VEGF) and vascular adhesion molecule (VCAM). Thus small molecules like the cotransins pose significant potential upon which to base the development of novel cancer therapeutics;however, a more complete understanding of cotransin activity, its mechanism of action and potential targets is needed. I propose to develop synthetic strategies for the late-stage diversification of cotransin-related cyclodepsipeptides in order to generate small molecule libraries containing unprecedented diversity. Evaluation of these molecules in cell-based and in vitro translocation assays will reveal optimal structural features for potent and selective inhibition of the secretion of cancer-relative proteins, including but not limited to VEGF and VCAM. Additionally, library members will be used in a cell-based proteomics approach to further identify protein targets whose secretion is inhibited by these small molecules. Relevance to Public Health: Despite decades of intense research, cancers remain a devastating set of diseases for which there is often no cure. We aim to identify small molecule therapeutics that block the secretion, and hence the functional expression of multiple proteins involved in tumor angiogenesis and tumor cell survival.